To run locally in a way that matches the GitHub Pages:

1. Install everything based on the dependencies specified here by running the command bundle install
2. bundle exec jekyll serve --watch --baseurl ''
3. The site should be available at http://localhost:4000

Alternatively, you can develop against the Github Pages URL of your fork of the documentation repo. Just push to your gh-pages branch, and the site will be available at username.github.io/forked-repo-name.